If you use an FN P90 AEG as your primary, we always recommend the Tokyo Marui FN 57 Five-seveN Gas Blowback Pistol as the sidearm. In the real world, they have been designed to use the same ammo. The Marui airsoft version faithfully replicates the real pistol with the extenals mainly made of Polymer and the internals mainly allow. Mach Sakai takes a look at this pistol that was released over 10 years ago.